Words and designs are frequently printed onto clothing and other textile materials, as well as other objects. Common means of applying such designs to objects include the use of silk screens, and mechanically bonded thermal transfers. Silk screen processes are well known in the art, and a mechanical thermal process to textile materials is described in Hare, U.S. Pat. No. 4,244,358.
The use of computer technology has allowed almost instantaneous printing of images. For example, video cameras or scanning may be used to capture an image to a computer. The image may then be printed by any suitable printing means, including mechanical thermal printers, wet printed (inkjet) sublimation transfers and laser printers. These printers can print in multiple colors.
The process of thermal transfers by mechanical means is described in Hare, U.S. Pat. No. 4,773,953. The art, as developed under this patent, is well known and defined in practice. The resulting mechanical image, as transferred, is a surface bonded image with a raised plastic like feel to the surface. The resulting printed image is stiff to the feel, has poor dimensional stability when stretched and poor color range, providing the incentive to seek a better process to achieve a better result.
Sublimation ink solids change to a gas at about 350-400° F., and have a high affinity for polyester at the sublimation temperature and a limited affinity for most other materials. Sublimation is the process where the solid changes into a gas directly, without undergoing the normal liquid phase in between. Sublimation dyes get converted into gas from solid state as a result of the heat-transfer process. On applying heat and pressure, they subsequently get absorbed into the substrate on which the image is to permanently appear. Sublimation dyes form durable and virtually permanent images.
Printed matter can be generated by a number of processes and technologies, including flexographic, rotogravure, lithographic, and non-impact printing. Lithographic printing is a process which utilizes a coated metal or polymeric plate containing a hydrophobic image area which accepts, i.e., it is wetted by, hydrophobic based ink and a non-image hydrophilic area which accepts water, i.e., the fountain solution. As practiced in the prior art, high speed web presses use inks that contain organic solvents to transport the ink. The drying of the printed ink film is achieved by solvent volatilization at a substrate temperature of about 250-400° F. and, to some degree, by penetration of the ink oil into the paper, leaving behind a hard polymeric film. Consequently, the use of such inks in the prior art requires highly sophisticated emission control equipment in order to comply with clean air and occupational standards for exposure to organic solvents. Considering these environmental standards and the costs associated with complying with them under practical industrial conditions, artisans in the field of ink development have been vigorously engaged in the development of new inks that will more readily meet environmental standards but still provide the quality performance demanded for the final printed product.
A typical heat setting web offset ink will contain the following major components: (a) a high molecular weight ink resin to disperse the pigment and also to provide the toughness and gloss the ink requires on drying; (b) solvents to provide the fluidity to the ink before it is placed on the web and dried in an oven; (c) pigment; and (d) other minor components such as gellants, which provide structure to the ink, plasticizers (non volatile solvents), waxes, thickeners, and antioxidants.
The content of volatile organic compounds (VOC) in a lithographic ink is typically determined by EPA Method 24. A 0.3-0.5 gram sample of ink is heated to 110° C. for one hour and the weight loss (total volatiles), corrected for water content and exempt compounds, is used to determine VOC content. For inks that do not contain water or exempt compounds, the total volatiles is equivalent to the total VOC content. It is known in the art that there are lithographic inks which intentionally contain water, exempt compounds, or a combination of water and exempt compounds.
Sheetfed offset inks typically dry at room temperature by a combination of penetration and oxidation. Initial penetration of the ink oil into the paper or paper coating occurs very rapidly and it changes the ink composition sufficiently to induce precipitation of the polymer or resin-rich phase on the paper surface. Oxidation of the drying oils and/or resins also begins so that the ink film is sufficiently rigid to withstand limited mechanical forces and enables the job to be printed on the second side of the sheet very soon after completing the first side. Subsequently, further oxidation of the drying oils and/or resins further increases the rigidity of the ink film sufficiently to withstand rubbing and abrasion.
A typical sheetfed offset ink will contain the following major components: (a) a combination of resins such as a phenolic modified rosin ester and alkyds to disperse the pigment and also to provide the toughness and gloss the ink requires on drying; (b) oxidatively drying oils such as linseed oil; (c) high boiling paraffinic/naphthenic oils; (d) insoluble pigment(s), and (e) other minor components such as plasticizers (non volatile solvents), waxes, thickeners, and antioxidants. These inks contain some level of volatile content as a result of the high boiling paraffinic/naphthenic oil content. The typical percentage of volatile formulation components exceeds 10% by weight. Alternative sheetfed offset inks can be formulated without the use of volatile high boiling paraffinic/naphthenic oils, achieving a total volatile content of less than 10%.
There exists a specialized class of lithographic inks commonly referred to as “sublimation inks”. These ink formulations differ in that insoluble pigments are replaced with soluble colorants commonly known and referred to in the art as a heat activated or sublimation colorants. Sublimation dyes typically derive from two classes; disperse dyes and direct dyes. These dyes are prepared from organic systems that include azo, anthroquinone and phthalocyanine chemistry.
These colorants are activated or sublimed at a temperature in excess of about 350-400 degree F., which is generally above the operation temperature of the offset lithographic printing press used to generate the first printed substrate (or transfer sheet). This type of colorant is known to be well suited for use in creating transfer mediums. The sublimation colorant is printed onto the first substrate, but is not activated or sublimed. Upon the subsequent application of heat and contact pressure the sublimation-type colorant is activated or sublimed, and transfers from the first substrate to the second substrate. After transfer, the sublimed colorant is bound to the second substrate.
A problem with the current art is that ink formulations contain high levels of volatile organic compounds (VOC's). Typical VOC levels are in the range of 20-30%. Printers are required by various Federal, State, and Local environmental regulations to track and report VOC emissions.
An additional problem with the current art is that VOC's are retained in the printed sublimation transfer sheet. According to EPA's guidelines, 95% of the VOC's contained in a sheetfed printing ink (as supplied) are retained in the printed image on the sublimation transfer sheet. When the transfer sheet is processed with heat to activate and transfer the sublimable dye, these VOC's are released into the workplace.
The present invention uses a lithographic sublimation ink. Existing lithographic sublimation ink technology employs the use of volatile organic compounds in excess of 10% by weight (typically as much as 20-30% by weight). Volatile organic compounds (VOC's) are undesirable components of printing inks as they are regulated materials under EPA regulations and cause detrimental environmental effects. Thus, it is desirable to design a lithographic sublimation ink which contains minimal VOC content.
U.S. Pat. No. 5,431,721 describes lithographic ink resins and varnishes which employ non-volatile solvents.
U.S. Pat. No. 7,018,453 describes low VOC web offset heatset inks containing less than about 2 wt % of VOC containing an aqueous polymer latex dispersed in an ink base of a resin, a non-volatile plasticizer, and a pigment and method for preparing same.
U.S. Pat. No. 5,417,749 describes a printing ink useful for “waterless” printing processes comprising a water-in-oil microemulsion wherein the water phase is present in an amount of about 5 to 20 wt. %, based on the weight of the ink. The water phase contains about 0.5 to 3 wt. %, based on the weight of the ink, of a surfactant which will not lower the surface tension (as measured at ambient temperature) of the ink, but will preferably increase the surface tension of the ink by at least about 5%. The ink optionally contains about 0.05 to 0.5 wt. %, based on the weight of the ink, of a water-soluble polymer capable of producing a viscosity in the water phase of about 5 to 10 poise as measured at ambient temperature.
U.S. Pat. No. 6,200,372 describes a single fluid water-based offset lithographic news ink comprising water; a macromolecular resin binder comprised of a resin soluble in water regardless of the pH of the water, a rosin salt resin soluble in water at pH ranging from 7.5 to 10 and an aqueous emulsion polymer; pigment; a water dispersible soy bean based polymer; and a hydroxyethylethylene urea re-wetting agent.
U.S. Pat. No. 6,709,503 describes a waterbased heatset offset lithographic ink comprising water, polyamide resins or fumarated rosin resins, hydroxyethylethylene urea, a modified linseed oil, a dibutylated benzoguanamine, a pigment and p-toluene sulfonic acid.
U.S. Patent Publication No. 2009/0214790 describes a method of making an ink-printed fibrous web by applying onto at least one side of a coated fibrous web at least one ink layer of a planographic ink to form an image thereon to produce a printed fibrous web. The ink layer(s) has a total volatile content, as supplied, of less than 10% (preferably less than 5%). These inks utilize insoluble pigments rather than sublimable colorants.
Other patent literature in the field includes Japanese Patent Publication JP 2001026735, Japanese Patent Publication JP 3247677, U.S. Pat. No. 5,158,606, and Japanese Patent Publication JP 5287228.
Patent Publication No. WO 2005113694 describes an emulsion composition that comprises water, a hydrocarbon distillate having a boiling point of 215 to 325° C., and a surfactant having a hydrophilic lipophilic balance number of 10 or less. A vehicle composition, an ink composition, a lithographic printing process and a method to improve a lithographic printing process comprise the emulsion composition which when used in a lithographic printing ink can reduce emission of volatile organic compounds and reduce the time at start-up to establish print quality.
In summary, prior art examples are based on insoluble pigmented systems rather than soluble sublimable dyes, and are not suitable for sublimation printing. Thus, there is still a need for the lithographic printing of sublimation inks on a medium which provide an environmental benefit of low volatile organic compounds (VOC's).